;Exercise 1.9
(define (+ a b)
  (if (= a 0)
      b
      (inc (+ (dec a) b))))
(+ 4 5)
(inc (+ (dec 4) 5 ))
(inc (+ 3 5))
(inc (inc (+ (dec 3) 5)))
(inc (inc (+ 2 5)))
(inc (inc (inc (+ (dec 2) 5 ))))
(inc (inc (inc (+ 1 5 ))))
(inc (inc (inc (inc (+ (dec 1) 5 )))))
(inc (inc (inc (inc (+ 0 5 )))))
(inc (inc (inc (inc 5))))
(inc (inc (inc 6)))
(inc (inc 7))
(inc 8)
9
;Este processo é recursivo.

(define (+ a b)
  (if (= a 0)
      b
      (+ (dec a) (inc b))))
(+ 4 5)
(+ (dec 4) (inc 5))
(+ 3 4)
(+ (dec 3) (inc 6))
(+ 2 7)
(+ (dec 2) (inc 7))
(+ 1 8)
(+ (dec 1) (inc 8))
(+ 0 9)
9
;Este processo é iterativo.
